In the brewing industry milling of raw materials prior to mashing in for wort production is usually done by one of the following techniques:                dry milling by roller mill        dry milling by hammer mill        wet milling by steeping and roller mill        conditioned milling (similar to dry milling by roller mill, except that malt moisture level is raised slightly to make the husks of the grains more pliable.        dispersion pump milling        
Each of these operations has its advantages and drawbacks in terms of extract yield, oxygen pick-up, separation performance on mash separation, effect on downstream processing, enzymatic performance of grist (mashing time), hygienic aspects, power consumption, dust explosion risks, extraction of tannins from husks, filtration run-off etc.
Wet milling has become less popular due to some major disadvantages associated with this kind of milling technique, notably long residence time distributions for the mash and insufficient milling of poorly modified malts. However, wet milling also has some significant advantages over dry milling. Increased safety regulations with respect to dust explosion risks, for instance, necessitate preventive measures that have driven up the cost of dry milling operations. Wet milling techniques obviously do not require such measures.
The inventors have investigated dispersion pump technology as a possible alternative to dry milling. However, the abrasion of the stator rotor combination due to non-malt particles was found to result in high maintenance costs and unreliable performance.
Hence, there is a need for a milling technique that combines the advantages of wet milling (no dust, minimal safety precautions, simple equipment, low capital expenditure) with the simplicity of e.g. the hammer mill process.